Debinderizer for rapidly removing binder from a green body

ABSTRACT

The disclosure relates to a system for removing binder from &#34;green&#34; bodies wherein debinding action takes place substantially uniformly throughout the sytem for large load as well as for small loads. This result is obtained by providing a plurality of shelves for holding the parts and providing turbulent atmosphere flow across all shelves with recirculation taking palce over a water fall in the system to provide both a water saturated atmosphere and removal of binder from the atmosphere and system simultaneously.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a debinderizer for rapidly removing binderfrom a green body composed of fine particles of metal or ceramic and abinder system without causing swelling of the binder system while withinthe interstices of the green body and for removal of substantially allcarbon formed during removal of the binder caused by pyrolysis and/orother reasons and to the method of providing a beneficial atmospherestream path.

2. Description of the Prior Art

The art of forming articles from metal and ceramic particulate materialis well known and examples of such systems are represented in the priorart patents of Strivens, U.S. Pat. Nos. 2,939,199, Curry 4,011,291,Wiech 4,404,166, the European application of Wiech (81100209.6,published July 22, 1981), Wiech U.S. Pat. No. 4,661,315 and others. Inaccordance with the procedures set forth in the disclosures in the abovenoted patents and European application, debinderizing and sintering haveproceeded without any substantial problem with varying degrees of speedas long as the debinderizer load was small relative to the load capacityof the debinderizer. However, it was found that a carbon build-updeveloped both on the surface of as well as within the part being formedfor large loads as stated in the above noted Wiech U.S. application.This problem was minimized to a great degree and debinderizing speedincreased by the addition of water to the system as stated in said WiechU.S application using prior art debinderizers. However, upon inspection,it was noted that sintered parts positioned within the debinderizer andremote from the direct path of recirculating atmosphere therein did notbenefit from the carbon reduction and debinding speed to the same extentas the parts which were directly in the path of the moving atmosphere.This presented a yield problem which was undesirable. It is thereforeapparent that a system and/or procedure which will improve the yieldwithout adding offsetting problems is highly desirable.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the present invention, the above noted problem isminimized and there is provided a debinderizer and atmosphere flow pathwherein binder is rapidly removed from "green" parts at substantiallyall locations within the debinderizer and wherein yields obtained perunit volume of debinderizer are much larger than those obtained in priorart debinderizers.

Briefly, in accordance with the present invention, there is provided abebinderizer in the form of an oven having a plurality of shelvesdisposed one above the other to hold "green" parts. Openings areprovided at opposite ends of each shelf to permit turbulent flow of theatmosphere along each shelf and over and around the "green" bodiessitting thereon at high speed. External atmosphere, such as air, asneeded, enters the oven through a closable opening, mixes withrecirculating atmosphere, and circulates over a water holding containerand water fall to substantially saturate said atmosphere with watervapor. The saturated atmosphere is blown at high speed in a turbulentmanner by a blower through a heater wherein the atmosphere is heated andthen travels across the shelves in a direction parallel thereto to applythe saturated atmosphere in intimate contact with the green bodies,whereupon the atmosphere absorbs binder, leaves the shelf area, takes onexternal atmosphere as needed and recirculatres back over the waterholding container and water fall system.

The water holding container and water fall system comprises an upperwater holding tank into which water flows from an external source, thetemperature of which is substantially below the boiling point of thecomponents of the binder system and possibly some or all of the productsof binder decomposition. The container has a lower side wall over whichthe water eventually falls and travels along an incline to a lowercontainer, the recirculating atmosphere passing over both containers andthe incline to vaporize most of said water. The water in the containersis sufficiently cool to cause the volatilized binder and some or all ofthe products of binder decomposition to condense therein and eventuallyfall to the bottom of the lower container. These condensed componentspass, in the liquid or solid state, from the lower container to anenclosed container external of the oven along with some of the water andatmosphere under the influence of an external blower, the gases in thelower container being driven therefrom by a blower. The external blowercreates a partial vacuum in the external container which pulls theliquified binder out of the oven along with some of the water and ovenatmosphere. The oven is encased in a metal housing with Kaowool, aceramic fiber insulator with high temperature capability to about 2300°F. being disposed between the housing and the oven to provide theinsulation thereto.

The above described arrangement provides a recirculating water saturatedatmosphere which moves at high speed and passes evenly and aroundsubstantially all "green bodies" in the oven to provide a unifrom andhigh degree of binder removal and a high degree of water reaction withany carbon formed by pyrolytic decomposition of the binder or otherwisein conjunction with all of the "green" bodies in the system.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a schematic showing a debinderizer in accordance with thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the Figure, there is a schematic showing of adebinderizer in accordance with the present invention. The debinderizerincludes an outer steel housing 1, an oven 5 within the housing andinsulation 3 between the housing and the oven. The insulation can be anymaterial which is capable of withstanding temperatures which will beobserved within the oven. A preferred insulating material is aproprietary product known as Kaowool which is a ceramic fiber insulatorwith a high temperature capability of up to about 2300° F. The oven 5includes a closable opening 7 from the oven exterior thereinto throughthe oven outer surface 9, the latter being formed of steel sheet. Theoven 5 and debinderizer and preferably in the shape of a rectangularparallelepiped though the shape is not critical. For example, aspherical or ovoid shape can also be used.

A plurality of stacked shelves 11 are positioned and secured within ashelf holder 13 having air passages 15 at opposite ends thereof todirect the travel of circulated atmosphere within the oven from one endof the shelf holder 13 to the other end thereof in a directionsubstantially parallel to the shelves 15, to thereby surround and removebinder from the "green" bodies disposed on the shelves. A heatingelement 17 is positioned within the oven 5, preferably in the path ofatmosphere flow and just before the atmosphere stream enters the shelfholder 13. A blower 19 is positioned within the oven 5 and directs watersaturated atmosphere toward the heating element 17 and also provides theatmosphere stream with the oven with an increased flow rate to provide aturbulent atmosphere stream when the stream passes over the "green"bodies on the shelves 11.

A water source 21 is provided external of the housing 1 to provide waterthrough the valve 23 to an upper container 25 positioned within the oven5 at the bottom thereof and directly in the atmosphere stream. The waterwill be sufficiently cool in order to cause condensation of binder andbinder reaction products therein as is discussed hereinbelow.

The container 25 has a lowered side wall 37 at the upstream side thereofwith an incline 27 extending from the wall 37 to a lower container 29,overflow water from container 25 passing over the incline 27 to thecontainer 29. The lower container 29 and the incline 27 are alsopositioned directly in the path of atmosphere flow in order to saturateor at least humidify the atmosphere as it passes thereover. Sinceatmosphere contacting the water in container 25 or 29 or on the incline27 will normally have volatilized binder or reaction products of thepyrolytic decomposition of the binder therein, such volatilizedproducts, where appropriate, will condense in the water and graduallyflow, either in the liquid or solid state, to the bottom of container29.

A passageway 31 is provided at the base of the container 29 whichempties into enclosed container 33 to pass liquid and solid binder andreaction products thereof from the bottom of container 29 to container33. In addition, some atmosphere from oven 5 and water may pass alongpassageway 31 to container 33. A blower 35 communicates with theinterior of container 33 to provide a partial vacuum therein, therebycausing the materials noted above which flow in passageway 31 to bepulled into container 33. The container 33 will thereby be a collectionpoint for spent binder and any non-gaseous reaction products of binderdecomposition. Any volatiles that enter container 33 via passageway 31will be exhausted to the external atmosphere through or under theinfluence of blower 35. The bulk of any effluent particulates areretained in the water in container 33.

In actual operation, "green" bodies of the type disclosed in the priorart, as noted hereinabove and elsewhere, are placed on the shelves 11,the heater 17 is operated according to a predetermined temperatureprofile and the blower 19 is operated to cause an atmosphere stream topass from the blower, over the heater and then along the shelves 11 in aturbulent and high speed flow around the "green" bodies to remove anyliquid binder on the surface thereof as well as products of binderdecomposition. The atmosphere then travels out of the shelf area andpast the air inlet 7, where it takes on air in an amount sufficient tocompensate for any loss of air at passageway 31. The atmosphere streamthen passes over the water in container 29, the incline 27 and thecontainer 25 to pick up moisture and to permit any volatiles whichcondense at the temperature of the water to condense into the water atone of the water locations. The moisturized air will continue along thesomewhat circular, continuous path and will gradually become moresaturated with each pass of the water up to substantially the saturationpoint. The condensed volatiles as well as particulates, water and airwill also pass to container 33 via passageway 31 to remove binder andbinder reaction products from the oven 5 on-line. As stated above, anyparticulates are retained in the water in container 33.

If desired, in the event an atmosphere other than air is required in theoven 5, the opening 7 can be closed and replaced with an input system ofan appropriate atmosphere. For example, if an inert atmosphere isdesired, an external tank of argon with a valve can be provided in placeof the air input 7. In the case where a reducing atmosphere is required,the argon tank and valve can be supplemented with a hydrogen tank andvalve.

It can be seen that there has been provided a debinderising system andmethod wherein the atmosphere is forced at high speed and with turbulentflow over the surfaces of "green" bodies with all of the "green" bodieshaving substantially equal access to the atmosphere stream, therebyproviding uniformity and a high final yield of parts relative to priorart systems.

Though the invention has been described with respect to a specificpreferred embodiment thereof, many variations and modifications willimmediately become apparent to those skilled in the art. It is thereforethe intention that the appended claims be interpreted as broadly aspossible in view of the prior art to include all such variations andmodification.

I claim:
 1. A debinderizing system which comprises:(a) a housing, (b) acontinuous defined atmosphere path within said housing having anatmosphere therealong, (c) means in said atmosphere path for applyingwater to said atmosphere, (d) heating means for heating said atmosphere,(e) sample holding means in said atmosphere path for holding samples,and (f) means for causing said atmosphere to move along said atmospherepath at sufficient velocity to provide turbulent flow along the surfaceof samples at said sample holding means.
 2. The system of claim 1wherein said holding means comprises means for directing passage of saidatmosphere therethrough along defined subpaths.
 3. The system of claim 2wherein said holding means comprises plural stacked parallel shelves andmeans to direct said atmosphere across each of said shelves in the samedirection.
 4. A debinderizing system which comprises:(a) a housing, (b)a continuous defined atmosphere path with said housing having anatmosphere therealong, (c) means in said atmosphere path for applyingwater to said atmosphere, (d) heating means for heating said atmosphere,(e) holding means in said atmosphere path, and (f) means for causingsaid atmosphere to move along said atmosphere path at sufficientvelocity to provide turbulent flow at said holding means, (g) whereinsaid means for applying water to said atmosphere comprises a first waterholding container, a second water holding container upstream of anddisposed below said first water holding container, an incline betweensaid first and second containers, open to said atmosphere path, forpassing overflow water from said first container to said secondcontainer and means to supply water to said first container.
 5. Thesystem of claim 4 wherein said holding means comprises means fordirecting passage of said atmosphere therethrough along definedsubpaths.
 6. The system of claim 4 wherein said holding means comprisesplural stacked parallel shelves and means to direct said atmosphereacross each of said shelves in the same direction.
 7. The system ofclaim 4 further including means coupled to said means for applying waterto said atmosphere for removing condensed materials in said means forapplying water to a location external of said housing.
 8. The system ofclaim 5 further including means coupled to said means for applying waterto said atmosphere for removing condensed materials in said means forapplying water to a location external of said housing.
 9. The system ofclaim 6 further including means coupled to said means for applying waterto said atmosphere for removing condensed materials in said means forapplying water to a location external of said housing.
 10. The system ofclaim 7 wherein said means coupled includes a third container externalof said housing, a passageway between said third container and saidmeans for applying water and means for applying a partial vacuum alongsaid passageway from said third container to remove said condensedmaterials along said passageway from said means for applying water tosaid third container.
 11. The system of claim 8 wherein said meanscoupled includes a third container external of said housing, apassageway between said third container and said means for applyingwater and means for applying a partial vacuum along said passageway fromsaid third container to remove said condensed materials along saidpassageway from said means for applying water to said third container.12. The system of claim 9 wherein said means coupled includes a thirdcontainer external of said housing, a passageway between said thirdcontainer and said means for applying water and means for applying apartial vacuum along said passageway from said third container to removesaid condensed materials along said passageway from said means forapplying water to said third container.
 13. A debinderizing system whichcomprises:(a) a housing, (b) a continuous defined atmosphere path withinsaid housing having an atmosphere therealong, (c) means in saidatmosphere path for applying water to said atmosphere, (d) heating meansfor heating said atmosphere, (e) holding means in said atmosphere path,and (f) means for causing said atmosphere to move along said atmospherepath at sufficient velocity to provide turbulent flow at said holdingmeans, (g) further including means coupled to said means for applyingwater to said atmosphere for removing condensed materials in said meansfor applying water to a location external of said housing.
 14. Thesystem of claim 13 wherein said means coupled includes a third containerexternal of said housing, a passageway between said third container andsaid means for applying water and means for applying a partial vacuumalong said passageway from said third container to remove said condensedmaterials along said passageway from said means for applying water tosaid third container.
 15. The system of claim 13 wherein said holdingmeans comprises means for directing passage of said atmospheretherethrough along defined subpaths.
 16. The system of claim 13 whereinsaid holding means comprises plural stacked parallel shelves and meansto direct said atmosphere across each of said shelves in the samedirection.
 17. The system of claim 15 wherein said means coupledincludes a third container external of said housing, a passagewaybetween said third container and said means for applying water and meansfor applying a partial vacuum along said passageway from said thirdcontainer to remove said condensed materials along said passageway fromsaid means for applying water to said third container.
 18. The system ofclaim 16 wherein said means coupled includes a third container externalof said housing, a passageway between said third container and saidmeans for applying water and means for applying a partial vacuum alongsaid passageway from said third container to remove said condensedmaterials along said passageway from said means for applying water tosaid third container.